The half-wave dipole is the simplest practical antenna – two wires fed in the middle. Its resonant length is slightly shorter than half a wavelength because of end effects, which is why amateur radio operators use the famous 468/f rule.
How to use the Dipole Antenna Calculator
- Frequency f
- End-effect (shortening) factor K
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the frequency and the end-effect factor (0.95 for thin wire; lower for thick conductors).
Inputs explained
| Field | What to enter |
|---|---|
| Frequency f | Units: MHz, kHz, GHz |
| End-effect (shortening) factor K | A number |
What each result means
- Wavelength λ = 299792458÷[Frequency f]
- Total dipole length = [End-effect (shortening) factor K]×299792458÷[Frequency f]÷2
- Length of each leg = [End-effect (shortening) factor K]×299792458÷[Frequency f]÷4
Example values
How the main result changes when Frequency f changes and everything else stays at the example values above:
| Frequency f (MHz) | Total dipole length (m) |
|---|---|
| 7.1 | 20.0565 |
| 10.65 | 13.371 |
| 14.2 | 10.0283 |
| 17.75 | 8.0226 |
| 21.3 | 6.6855 |
| 28.4 | 5.0141 |
Formula
λ = c/f, L_total = K·λ/2, leg = L_total/2 (K ≈ 0.95 for wire; L(ft) ≈ 468/f(MHz))
Worked example
Inputs — Frequency f: 14.2 MHz; End-effect (shortening) factor K: 0.95.
Results — Wavelength λ = 21.11214 m; Total dipole length = 10.02827 m; Length of each leg = 5.01413 m.
Key terms
- Half-wave dipole
- Antenna about half a wavelength long.
Frequently asked questions
What is the 468 rule?
Total length in feet ≈ 468 / frequency in MHz.
Why is the dipole shorter than λ/2?
End effects and conductor thickness lower the resonant frequency.
What is the feed-point impedance?
About 73 Ω in free space, lower near the ground.
How do I tune it?
Trim the ends equally until the SWR is lowest at your frequency.